I think there's at least one company that provides something like this but hides its own caches. I don't see a problem with that, but to charge to take people to caches listed on a listing site certainly isn't something I would approve of, but as Matt (nobby) has said, there's not much we could do about it.
If I knew that a company was doing that in an area where I own caches I'd contact the company and ask them not to visit mine. If they weren't co-operative I'd try to find out whether it was happening on specific dates, and if it was I'd temporarily disable my caches on and a bit before those dates.
I'm not sure that making the caches PM only would work, as the company could very well be a PM itself.
Do not go gentle into that good night.
Rage, rage against the dying of the light. (Dylan Thomas)